In broadest terms, the aim of this research program is to investigate the characteristics of afferent somatosensory volleys at all "levels" within the mammalian CNS, to discover and to understand how sensory information is encoded, transmitted and processed within the system. This requires an adequate description of the distribution and arrangement of neurons with different functional properties, a quantitative estimate of the convergence and divergence of afferent fibers within the different classes of neurons, a "complete" description of the functional properties common to all or some classes, and unique to the different classes, of neurons, and an estimate of the interaction among the various classes of neurons. Single neuron isolation, gross potential recording, anatomical and histochemical techniques are relevent to attaining these research objectives, the major emphasis being on extracellular technique. Functional sets of neurons will be identified at each "level" of the system, their membership in any set being defined by the pattern of their synaptic input(s), their specific response properties, and the site(s) of their axonal termination(s). The experimental designs allow determination of their interconnections, both within and between "levels", so that "wiring diagrams" may be constructed for the system. Attempts will be made to form a one-to-one correspondence between functional set and structural type. Considerable attention will also be devoted to "natural" stimulus sensitivities. The principal preparation will be a fully anesthetized cat, although chronic, waking preparations and other species will be used as the experiments demand.